It is known from U.S. Pat. No. 3,917,574, issued Nov. 4, 1975 to Gibbs et al., to make substantially linear water-soluble interpolymeric interfacially spreading polyelectrolytes of the type contemplated herein in a continuous addition solution polymerization process wherein at least one ionic hydrophilic monomer and at least one nonionic hydrophobic monomer in a polar mutual solvent are added to a polymerization reactor at a rate no greater than the rate of polymerization and in a ratio which is substantially equal to that desired in the resulting polymer phase.
It is also known from U.S. Pat. No. 3,965,032, to make such substantially linear interpolymeric interfacially spreading polyelectrolytes by polymerization of a functional nonionic monomeric mixture in a nonaqueous solvent, followed by isolation of the polymer and subsequent conversion to an ionic derivative.
It is often the case when copolymerizing ionic and nonionic monomers that the monomers are not present in the same phase during polymerization and more than one polymerization reaction is occurring. The reaction mixture forms two phases with the ionic monomers preferentially distributed in one phase and the nonionic monomers in the other. Polymerization can take place simultaneously in both phases, forming a complex mixture of highly charged water-soluble polymer and slightly charged essentially nonionic polymer.
Further, only a limited number of solvents are available which can compatibilize nonionic and ionic species and such solvents are usually expensive and difficult to separate from the polymer.
In addition, monomer removal is a problem in purifying these mixtures. For ecological and health reasons, even low levels of monomers are not permissible. Since solution reactions rarely go to high conversion, the unreacted monomer must be separated from the polymer. The simplest way is to strip off the monomers and solvent, then redissolve the polymer in water for subsequent use. But ionic monomers are nonvolatile. Therefore, they must be removed by fractional precipitation extraction or dialysis. And, since in most cases any polymeric surfactant synthesized will be soluble in the same solvents as the monomer, dialysis is the only practical approach.
Added to the above problems are the fact that ionic monomers are often difficult to prepare, purify and store and very often undergo small amounts of homopolymerization wherein the homopolymer cannot be removed from the monomer and ends up as a contaminant in the final product.
Additional related prior art includes U.S. Pat. Nos. 3,178,396 and 3,072,588 which disclose the reaction of a high molecular weight polymer of vinyl benzyl chloride in the form of an anionic latex, with a nucleophile to obtain a water-soluble product. Such processes, however, yield products of very high molecular weight which are contaminated with anionic surfactants, and therefore are not useful as polyelectrolytes as contemplated herein.